Science >> Chemistry for Kids Naming Chemical Compounds Chemical compounds are formed when elements are joined by chemical bonds. These bonds are so strong that the compound behaves like a single substance. Compounds have their own properties that are unique from the elements they are made of. A compound is a type of molecule with more than one element. You can go here to learn more about molecules and compounds. How Compounds are Named Chemists have a specific way of naming compounds. It is a standard method of naming compounds that is used by scientists around the world. The name is built from the elements and the construction of the molecule. Basic Naming Convention First we’ll cover how to name molecules with two elements (binary compounds). The name of a compound with two elements has two words. To get the first word we use the name of the first element, or the element to the left of the formula. To get the second word we use the name of the second element and change the suffix to «ide» at the end of the word. Some examples of adding the «ide»: O = oxygen = oxide
Cl = chlorine = chloride
Br = bromine = bromide
F = fluorine = fluoride Examples of binary compounds: NaCl — sodium chloride
MgS — magnesium sulfide
InP = indium phosphide What if there is more than one atom? In cases where there is more than one atom (for example there are two oxygen atoms in CO2) you add a prefix to the start of the element based on the number of atoms. Here is a list of the prefixes used:

# Atoms
1
2
3
4
5
6
7
8
9
10
Prefix
mono-
di-
tri-
tetra-
penta-
hexa-
hepta-
octa-
nona-
deca-

** note: the «mono» prefix is not used on the first element. For example CO = carbon monoxide. Examples: CO2 = carbon dioxide
N2O = dinitrogen monoxide
CCL4 = carbon tetrachloride
S3N2 = trisulfur dinitride How is the order of the elements determined? When there are two elements in a compound, which element goes first in the name? If the compound is made of a metal element and a nonmetal element, then the metal element is first. If there are two nonmetal elements, then the first name is the element to the left side of the periodic table. Examples:

  • In a compound that contains iron and fluoride, the metal (iron) would go first.
  • In a compound that contains carbon and oxygen the element to the left on the periodic table (carbon) would go first.

More Complex Naming Rules See below for some of the more complex naming rules. Naming Metal-Nonmetal Compounds If one of the two compounds is a metal, then the naming convention changes a bit. Using the stock method, a roman numeral is used after the metal to indicate which ion is using the charge. Examples: Ag2Cl2 = silver (II) dichloride
FeF3 = iron (III) fluoride Naming Polyatomic Compounds Polyatomic compounds use a different suffix. Most of them end in «-ate» or «-ite». There are a few exceptions that end in «-ide» including hydroxide, peroxide, and cyanide. Examples: Na2SO4 = sodium sulfate
Na3PO4 = sodium phosphate
Na2SO3 = sodium sulfite Naming Acids Hydro acids use the prefix «hydro-» and the suffix «-ic». HF = hydrofluoric acid
HCl — hydrochloric acid Oxoacids containing oxygen use the «-ous» or the «-ic» suffix. The «-ic» suffix is used for the acid that has more oxygen atoms. H2SO4 = sulfuric acid
HNO2 = nitrous acid
HNO3 = nitric acid Activities Take a ten question quiz on this page. Listen to a reading of this page: More Chemistry Subjects Elements and the Periodic Table
Elements
Periodic Table Science >> Chemistry for Kids

Video transcript

— [Instructor] Let’s get
some practice now thinking about how ions typically form, how they might form compounds and how we name those compounds. So let’s start with
something in group one. In this first column, this
first column is often known as alkali metals. So let’s start with potassium. K is the symbol for potassium. Now things in group one here, one way to think about
is their outermost shell has one electron in it. So they wouldn’t mind
losing that electron. So when they ionize, they
tend to lose an electron and become a cation, a positive ion. And so let’s look at a situation
where I have some potassium that has been ionized. I could write it just like this, we’ve seen that in previous videos and we can refer to this
just as a potassium ion, we could refer to this
as potassium one plus. We could refer to this
as a potassium cation. Now let’s go on to the other
side of the periodic table. Things that would really
love to grab an electron. So things in group, in the halides, which is this column right over here. So these are the halides. They have seven electrons
in their outermost shell. They would love to have eight, so they tend to be really
good at grabbing electrons. And so let’s say we’re
dealing with chlorine, and chlorine is able to ionize. So it’s able to grab an electron. When chlorine grabs an electron, it will be a negatively charged ion, so you could write it
as Chlorine one minus, but the way that we
generally refer to an anion, a negatively charged ion, instead of just calling
this the chlorine anion, we would call this chloride. So this we would refer to as Chloride. Now as you can imagine
with potassium having a positive one charge or one plus charge and this having a negative charge, they’re going to be
attracted to each other and they can actually
form an ionic compound. The ionic compound they
would form, we would write as, you’d write your positive ion first and then you would
write your negative ion. And this right over
here would be described as potassium chloride. Let me write that down. Potassium, potassium chloride. Now you might be saying, «Well, I just,» Let me rewrite the whole thing. So you know the chloride
part, you say okay, this is going to be an anion because instead of writing chlorine which is the name of this element, I wrote this IDE at the end to say, «Hey, this is an anion,» so I know that this is the
chlorine anion, this is chloride, why didn’t I do something
similar for potassium? Well, the way the convention works is if someone says potassium chloride, you know you’re dealing
with an ionic compound and if the chlorine has
a negative one charge, an ionic compound, the whole thing is gonna be neutral. So if this one over here is one minus, then you know this over
here is just one-for-one, this is going to be one plus so you know that you’re
dealing with a potassium cation and you could say and a chloride
ion or a chlorine anion. You could refer to it various ways, but this is potassium chloride. You have a positively charged potassium and you have a negatively
charged chlorine, which we would call a chloride. In the next few videos I’ll
do many, many more examples of this and ones that will be
a little bit more complicated.

Learning Outcomes

  • Derive names for common types of inorganic compounds using a systematic approach

Nomenclature, a collection of rules for naming things, is important in science and in many other situations. This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO3, and N2O4. The simplest of these are binary compounds, those containing only two elements, but we will also consider how to name ionic compounds containing polyatomic ions, and one specific, very important class of compounds known as acids (subsequent discussion in this text will focus on these compounds in great detail). We will limit our attention here to inorganic compounds, compounds that are composed principally of elements other than carbon, and will follow the nomenclature guidelines proposed by IUPAC. The rules for organic compounds, in which carbon is the principle element, will be treated in the module on organic chemistry.

Ionic Compounds

To name an inorganic compound, we need to consider the answers to several questions. First, is the compound ionic or molecular? If the compound is ionic, does the metal form ions of only one type (fixed charge) or more than one type (variable charge)? Are the ions monatomic or polyatomic? If the compound is molecular, does it contain hydrogen? If so, does it also contain oxygen? From the answers we derive, we place the compound in an appropriate category and then name it accordingly.

Compounds Containing Only Monatomic Ions

The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix –ide). Some examples are given in Table 1.

Table 1. Names of Some Ionic Compounds
NaCl, sodium chloride Na2O, sodium oxide
KBr, potassium bromide CdS, cadmium sulfide
CaI2, calcium iodide Mg3N2, magnesium nitride
CsF, cesium fluoride Ca3P2, calcium phosphide
LiCl, lithium chloride Al4C3, aluminum carbide

Compounds Containing Polyatomic Ions

Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, except there is no need to change to an –ide ending, since the suffix is already present in the name of the anion. Examples are shown in Table 2.

Table 2. Names of Some Polyatomic Ionic Compounds
KC2H3O2, potassium acetate (NH4)Cl, ammonium chloride
NaHCO3, sodium bicarbonate CaSO4, calcium sulfate
Al2(CO3)3, aluminum carbonate Mg3(PO4)2, magnesium phosphate

Ionic Compounds in Your Cabinets

Every day you encounter and use a large number of ionic compounds. Some of these compounds, where they are found, and what they are used for are listed in Table 3. Look at the label or ingredients list on the various products that you use during the next few days, and see if you run into any of those in this table, or find other ionic compounds that you could now name or write as a formula.

Table 3. Everyday Ionic Compounds
Ionic Compound Use
NaCl, sodium chloride ordinary table salt
KI, potassium iodide added to “iodized” salt for thyroid health
NaF, sodium fluoride ingredient in toothpaste
NaHCO3, sodium bicarbonate baking soda; used in cooking (and as antacid)
Na2CO3, sodium carbonate washing soda; used in cleaning agents
NaOCl, sodium hypochlorite active ingredient in household bleach
CaCO3 calcium carbonate ingredient in antacids
Mg(OH)2, magnesium hydroxide ingredient in antacids
Al(OH)3, aluminum hydroxide ingredient in antacids
NaOH, sodium hydroxide lye; used as drain cleaner
K3PO4, potassium phosphate food additive (many purposes)
MgSO4, magnesium sulfate added to purified water
Na2HPO4, sodium hydrogen phosphate anti-caking agent; used in powdered products
Na2SO3, sodium sulfite preservative

Compounds Containing a Metal Ion with a Variable Charge

Most of the transition metals can form two or more cations with different charges. Compounds of these metals with nonmetals are named with the same method as compounds in the first category, except the charge of the metal ion is specified by a Roman numeral in parentheses after the name of the metal. The charge of the metal ion is determined from the formula of the compound and the charge of the anion. For example, consider binary ionic compounds of iron and chlorine. Iron typically exhibits a charge of either 2+ or 3+ (see Molecular and Ionic Compounds), and the two corresponding compound formulas are FeCl2 and FeCl3. The simplest name, “iron chloride,” will, in this case, be ambiguous, as it does not distinguish between these two compounds. In cases like this, the charge of the metal ion is included as a Roman numeral in parentheses immediately following the metal name. These two compounds are then unambiguously named iron(II) chloride and iron(III) chloride, respectively. Other examples are provided in Table 4.

Table 4. Names of Some Transition Metal Ionic Compounds
Transition Metal Ionic Compound Name
FeCl2 iron(II) chloride
FeCl3 _ iron(III) chloride
Hg 2 O mercury(I) oxide
HgO mercury(II) oxide
SnF2 tin(II) fluoride
SnF 4 tin(IV) flouride

Out-of-date nomenclature used the suffixes –ic and –ous to designate metals with higher and lower charges, respectively: Iron(III) chloride, FeCl3, was previously called ferric chloride, and iron(II) chloride, FeCl2, was known as ferrous chloride. Though this naming convention has been largely abandoned by the scientific community, it remains in use by some segments of industry. For example, you may see the words stannous fluoride on a tube of toothpaste. This represents the formula SnF2, which is more properly named tin(II) fluoride. The other fluoride of tin is SnF4, which was previously called stannic fluoride but is now named tin(IV) fluoride.

Ionic Hydrates

Ionic compounds that contain water molecules as integral components of their crystals are called hydrates. The name for an ionic hydrate is derived by adding a term to the name for the anhydrous (meaning “not hydrated”) compound that indicates the number of water molecules associated with each formula unit of the compound. The added word begins with a Greek prefix denoting the number of water molecules (see Table 5) and ends with “hydrate.” For example, the anhydrous compound copper(II) sulfate also exists as a hydrate containing five water molecules and named copper(II) sulfate pentahydrate. Washing soda is the common name for a hydrate of sodium carbonate containing 10 water molecules; the systematic name is sodium carbonate decahydrate. Formulas for ionic hydrates are written by appending a vertically centered dot, a coefficient representing the number of water molecules, and the formula for water. The two examples mentioned in the previous paragraph are represented by the formulas [latex]\text{copper(II) sulfate pentahydrate}\text{ CuSO}_{4}\cdot{5}\text{H}_{2}\text{O}[/latex] [latex]\text{sodium carbonate decahydrate}\text{ Na}_{2}\text{CO}_{3}\cdot{10}\text{H}_{2}\text{O}[/latex]

Table 5. Nomenclature Prefixes
Number Prefix Number Prefix
1 (sometimes omitted) mono- 6 hexa-
2 from- 7 hepta-
3 tri- 8 octa-
4 tetra- 9 nona-
5 penta- 10 deca-

Example 1: Naming Ionic Compounds

Name the following ionic compounds, which contain a metal that can have more than one ionic charge:

  1. Fe2S3 _ _ _
  2. CuSe
  3. GaN
  4. MgSO4·7H2O
  5. Ti 2 (SO 4 ) 3

Check Your Learning

Write the formulas of the following ionic compounds:

  1. chromium(III) phosphide
  2. mercury(II) sulfide
  3. manganese(II) phosphate
  4. copper(I) oxide
  5. iron(III) chloride dihydrate

Erin Brokovich and Chromium Contamination

In the early 1990s, legal file clerk Erin Brockovich (Figure 1) discovered a high rate of serious illnesses in the small town of Hinckley, California. Her investigation eventually linked the illnesses to groundwater contaminated by Cr(VI) used by Pacific Gas & Electric (PG&E) to fight corrosion in a nearby natural gas pipeline. As dramatized in the film Erin Brokovich (for which Julia Roberts won an Oscar), Erin and lawyer Edward Masry sued PG&E for contaminating the water near Hinckley in 1993. The settlement they won in 1996—$333 million—was the largest amount ever awarded for a direct-action lawsuit in the US at that time. Figure 1. (a) Erin Brockovich found that Cr(IV), used by PG&E, had contaminated the Hinckley, California, water supply. (b) The Cr(VI) ion is often present in water as the polyatomic ions chromate, CrO42− (left), and dichromate, Cr2O72− (right). Chromium compounds are widely used in industry, such as for chrome plating, in dye-making, as preservatives, and to prevent corrosion in cooling tower water, as occurred near Hinckley. In the environment, chromium exists primarily in either the Cr(III) or Cr(VI) forms. Cr(III), an ingredient of many vitamin and nutritional supplements, forms compounds that are not very soluble in water, and it has low toxicity. But Cr(VI) is much more toxic and forms compounds that are reasonably soluble in water. Exposure to small amounts of Cr(VI) can lead to damage of the respiratory, gastrointestinal, and immune systems, as well as the kidneys, liver, blood, and skin. Despite cleanup efforts, Cr(VI) groundwater contamination remains a problem in Hinckley and other locations across the globe. A 2010 study by the Environmental Working Group found that of 35 US cities tested, 31 had higher levels of Cr(VI) in their tap water than the public health goal of 0.02 parts per billion set by the California Environmental Protection Agency.

Molecular (Covalent) Compounds

The bonding characteristics of inorganic molecular compounds are different from ionic compounds, and they are named using a different system as well. The charges of cations and anions dictate their ratios in ionic compounds, so specifying the names of the ions provides sufficient information to determine chemical formulas. However, because covalent bonding allows for significant variation in the combination ratios of the atoms in a molecule, the names for molecular compounds must explicitly identify these ratios.

Compounds Composed of Two Elements

When two nonmetallic elements form a molecular compound, several combination ratios are often possible. For example, carbon and oxygen can form the compounds CO and CO2. Since these are different substances with different properties, they cannot both have the same name (they cannot both be called carbon oxide). To deal with this situation, we use a naming method that is somewhat similar to that used for ionic compounds, but with added prefixes to specify the numbers of atoms of each element. The name of the more metallic element (the one farther to the left and/or bottom of the periodic table) is first, followed by the name of the more nonmetallic element (the one farther to the right and/or top) with its ending changed to the suffix –ide. The numbers of atoms of each element are designated by the Greek prefixes shown in above in Table 5. When only one atom of the first element is present, the prefix mono– is usually deleted from that part. Thus, CO is named carbon monoxide, and CO2 is called carbon dioxide. When two vowels are adjacent, the a in the Greek prefix is usually dropped. Some other examples are shown in Table 6.

Table 6. Names of Some Molecular Compounds Composed of Two Elements
Compound Name Compound Name
SO2 _ sulfur dioxide BCl3 _ boron trichloride
SO 3 sulfur trioxide SF 6 sulfur hexafluoride
NO2 _ nitrogen dioxide PF 5 phosphorus pentafluoride
N 2 O 4 dinitrogen tetroxide P 4 O 10 tetraphosphorus decaoxide
N2O5 _ _ _ dinitrogen pentoxide IF 7 iodine heptafluoride

There are a few common names that you will encounter as you continue your study of chemistry. For example, although NO is often called nitric oxide, its proper name is nitrogen monoxide. Similarly, N2O is known as nitrous oxide even though our rules would specify the name dinitrogen monoxide. (And H2O is usually called water, not dihydrogen monoxide.) You should commit to memory the common names of compounds as you encounter them.

Example 2: Naming Covalent Compounds

Name the following covalent compounds:

  1. SF 6
  2. N2O3 _ _ _
  3. Cl2O7 _ _ _
  4. P4O6

Check Your Learning

Write the formulas for the following compounds:

  1. phosphorus pentachloride
  2. dinitrogen monoxide
  3. iodine heptafluoride
  4. carbon tetrachloride

Binary Acids

Some compounds containing hydrogen are members of an important class of substances known as acids. The chemistry of these compounds is explored in more detail in later, but for now, it will suffice to note that many acids release hydrogen ions, H+, when dissolved in water. To denote this distinct chemical property, a mixture of water with an acid is given a name derived from the compound’s name. If the compound is a binary acid (comprised of hydrogen and one other nonmetallic element):

  1. The word “hydrogen” is changed to the prefix hydro-
  2. The other nonmetallic element name is modified by adding the suffix –ic
  3. The word “acid” is added as a second word

For example, when the gas HCl (hydrogen chloride) is dissolved in water, the solution is called hydrochloric acid. Several other examples of this nomenclature are shown in Table 7.

Table 7. Names of Some Simple Acids
Name of Gas Name of Acid
HF(g), hydrogen fluoride HF(aq), hydrofluoric acid
HCl(g), hydrogen chloride HCl(aq), hydrochloric acid
HBr(g), hydrogen bromide HBr(aq), hydrobromic acid
HI(g), hydrogen iodide HI( aq ), hydroiodic acid
H2S(g), hydrogen sulfide H2S(aq), hydrosulfuric acid

Oxyacids

Many compounds containing three or more elements (such as organic compounds or coordination compounds) are subject to specialized nomenclature rules that you will learn later. However, we will briefly discuss the important compounds known as oxyacids, compounds that contain hydrogen, oxygen, and at least one other element, and are bonded in such a way as to impart acidic properties to the compound (you will learn the details of this later). Typical oxyacids consist of hydrogen combined with a polyatomic, oxygen-containing ion. To name oxyacids:

  1. Omit “hydrogen”
  2. Start with the root name of the anion
  3. Replace –ate with –ic, or –ite with –ous
  4. Add “acid”

For example, consider H2CO3 (which you might be tempted to call “hydrogen carbonate”). To name this correctly, “hydrogen” is omitted; the –ate of carbonate is replace with –ic; and acid is added—so its name is carbonic acid. Other examples are given in Table 8. There are some exceptions to the general naming method (e.g., H2SO4 is called sulfuric acid, not sulfic acid, and H2SO3 is sulfurous, not sulfous, acid).

Table 8. Names of Common Oxyacids
Formula Anion Name Acid Name
HC2H3O2 _ _ _ _ _ acetate acetic acid
HNO3 _ nitrate nitric acid
HNO2 _ nitrite nitrous acid
HClO4 perchlorate perchloric acid
H2CO3 _ _ _ carbonate carbonic acid
H2SO4 sulfate sulfuric acid
H2SO3 _ _ _ sulfite sulfurous acid
H3PO4 phosphate phosphoric acid

Video Review: Language of Chemistry

Learning to talk about chemistry can be like learning a foreign language, but Hank is here to help with some straightforward and simple rules to help you learn to speak Chemistrian like a native. You can view the transcript for “How to Speak Chemistrian: Crash Course Chemistry #11” here (opens in new window).

Key Concepts and Summary

Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to –ide. For example, K2O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge. Thus, FeCl2 is iron(II) chloride and FeCl3 is iron(III) chloride. Some compounds contain polyatomic ions; the names of common polyatomic ions should be memorized. Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF6, sulfur hexafluoride, and N2O4, dinitrogen tetroxide. Acids are an important class of compounds containing hydrogen and having special nomenclature rules. Binary acids are named using the prefix hydro-, changing the –ide suffix to –ic, and adding “acid;” HCl is hydrochloric acid. Oxyacids are named by changing the ending of the anion to –ic, and adding “acid;” H2CO3 is carbonic acid.

Try It

  1. Name the following compounds:
    1. CsCl
    2. BaO
    3. K2S
    4. BeCl2
    5. HBr
    6. AlF 3
  2. Name the following compounds:
    1. NaF
    2. Rb 2 O
    3. BCl3 _
    4. H 2 See
    5. P4O6
    6. ICl 3
  3. Write the formulas of the following compounds:
    1. rubidium bromide
    2. magnesium selenide
    3. sodium oxide
    4. calcium chloride
    5. hydrogen fluoride
    6. gallium phosphide
    7. aluminum bromide
    8. ammonium sulfate
  4. Write the formulas of the following compounds:
    1. lithium carbonate
    2. sodium perchlorate
    3. barium hydroxide
    4. ammonium carbonate
    5. sulfuric acid
    6. calcium acetate
    7. magnesium phosphate
    8. sodium sulfite
  5. Write the formulas of the following compounds:
    1. chlorine dioxide
    2. dinitrogen tetraoxide
    3. potassium phosphide
    4. silver(I) sulfide
    5. aluminum nitride
    6. silicon dioxide
  6. Write the formulas of the following compounds:
    1. barium chloride
    2. magnesium nitride
    3. sulfur dioxide
    4. nitrogen trichloride
    5. dinitrogen trioxide
    6. tin(IV) chloride
  7. Each of the following compounds contains a metal that can exhibit more than one ionic charge. Name these compounds:
    1. Cr2O3 _ _ _
    2. FeCl2
    3. CrO3 _
    4. TiCl4
    5. CoO
    6. MoS2
  8. Each of the following compounds contains a metal that can exhibit more than one ionic charge. Name these compounds:
    1. NiCO3 _
    2. MoO3 _
    3. Co(NO 3 ) 2
    4. V2O5 _ _ _
    5. MnO2 _
    6. Fe2O3 _ _ _
  9. The following ionic compounds are found in common household products. Write the formulas for each compound:
    1. potassium phosphate
    2. copper(II) sulfate
    3. calcium chloride
    4. titanium dioxide
    5. ammonium nitrate
    6. sodium bisulfate (the common name for sodium hydrogen sulfate)
  10. The following ionic compounds are found in common household products. Name each of the compounds:
    1. Ca(H2PO4)2
    2. FeSO4
    3. CaCO3 _
    4. MgO
    5. NaNO2 _
    6. TO
  11. What are the IUPAC names of the following compounds?
    1. manganese dioxide
    2. mercurous chloride (Hg2Cl2)
    3. ferric nitrate [Fe(NO3)3]
    4. titanium tetrachloride
    5. cupric bromide (CuBr2)

Glossary

binary acid: compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water) binary compound: compound containing two different elements. nomenclature: system of rules for naming objects of interest oxyacid: compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)


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